CBSE Class 12th Physics Chapter 12 - Atoms Important Questions with Answers

You should focus on solving CBSE Class 12th Physics Chapter 12: Atoms important questions, especially to help you score high marks. By solving CBSE Class 12th Physics 12 questions, you will be solving exam-oriented questions only.

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CBSE Class 12th Physics Chapter 12 - Atoms is included in the 8th unit of the syllabus. Along with chapter 12, one other chapter is included in Unit 8, which is Nuclei. Unit 8, along with unit 7, that is, Dual Nature of Radiation and Matter, carries a total of 8 marks in the question paper. The following topics are included in the 12th chapter of the syllabus: Alpha-particle scattering experiment; Rutherford's model of the atom; Bohr model of the hydrogen atom, Expression for radius of nth possible orbit, velocity and energy of electron in nth orbit, hydrogen line spectra (qualitative treatment only). The theory paper will be conducted for 70 marks. 30 marks will be provided for the practical exam.

Since the exams are fast approaching, make sure to complete your curriculum on time to revise using the model test papers available on the official website of the Central Board of Secondary Education. Try to focus on completing your syllabus in the first 6 months of the academic year so that you have enough time to revise or clear your doubts with your tutors or teachers as soon as possible. Physics can be an intimidating subject, so try and make notes after the end of every lecture for an effective revision session at home. Note down important formulas and theorems where necessary. Always focus on understanding the topics rather than mugging up the answers. Use creative mediums to understand difficult topics, such as YouTube videos, and take online mock tests to assess your preparation level after completing your syllabus.

The Central Board of Secondary Education has recently released the class 12 date sheet, according to which the exams will be starting on 15th February 2025. The date sheet is now uploaded online at cbse.nic.in in a PDF format. While attempting the Physics question paper, do not forget to read the instructions carefully printed at the top of the question paper to understand the internal choices in the question paper.

Given below, we are sharing some CBSE Class 12th Physics Chapter 12 - Atoms Important Questions with Answers. Practice these questions since they have a high chance of appearing in the question paper.

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Define ionization energy.
How would the ionization energy change when electron in hydrogen atom is replaced by a particle of mass 200 times that of the electron but having the same charge? (All India 2016)

Question 2.

Calculate the shortest wavelength of the spectral lines emitted in Balmer series.
[Given Rydberg constant, R = 10⁷ m^-1] (All India 2016)

Question 3.

The electron, in a hydrogen atom, is in its second excited state.
Calculate the wavelength of the lines in the Lyman series, that can be emitted through the permissible transitions of this electron.
(Given the value of Rydberg constant, R = 1.1 × 107 m^-1) (Comptt. Delhi 2016)

Question 4.

An ?-particle moving with initial kinetic energy K towards a nucleus of atomic number z approaches a distance ‘d’ at which it reverses its direction. Obtain the expression for the distance of closest approach ‘d’ in terms of the kinetic energy of ?-particle K. (Comptt. All India 2016)

Question 5.

Find the ratio between the wavelengths of the ‘most energetic’ spectral lines in the Balmer and Paschen series of the hydrogen spectrum. (Comptt. All India 2016)

Question 6.

Define the distance of closest approach. An a-particle of kinetic energy ‘K’ is bombarded on a thin gold foil. The distance of the closest approach is V. What will be the distance of closest approach for an a-particle of double the kinetic energy? (Delhi 2016)

Question 7.

Write two important limitations of Rutherford nuclear model of the atom. (Delhi 2016)

Question 8.

Find out the wavelength of the electron orbiting in the ground state of hydrogen atom. (Delhi 2016)

Question 9.

Find the wavelength of the electron orbiting in the first excited state in hydrogen atom. (Delhi 2016)

Question 10.

A 12.5 eV electron beam is used to excite a gaseous hydrogen atom at room temperature. Determine the wavelengths and the corresponding series of the lines emitted. (All India 2016)

Question 1.

The short wavelength limit for the Lyman series of the hydrogen spectrum is 913.4 A Calculate the short wavelength limit for Balmer series of the hydrogen spectrum. (All India 2016)

Question 2.

The ground state energy of hydrogen atom is -13.6 eV. If an electron makes a transition from an energy level -1.51 eV to -3.4 eV, calculate the wavelength of the spectral line emitted and name the series of hydrogen spectrum to which it belongs. (All India 2016)

Question 3.

Calculate the shortest wavelength of light emitted in the Paschen series of hydrogen spectrum. Which part of the electromagnetic spectrum, does it belong to ? (Given : Rydberg constant, R = 1.1 × 10⁷ m^-1) (Comptt. Delhi 2016)

Question 4.

Calculate the shortest wavelength of photons emitted in the Bracket series of hydrogen spectrum. Which part of the e.m. spectrum, does it belong? [Given Rydberg constant, R = 1.1 × 10⁷ m^-1] (Comptt. Delhi 2016)

Question 5.

Calculate the longest wavelength of the photons emitted in the Balmer series of hydrogen spectrum. Which part of the e.m. spectrum, does it belong to?
[Given Rydberg constant, R = 1.1 × 107 m^-1]. (Comptt. Delhi 2016)

Question 6.

(i) State Bohr’s quantization condition for defining stationary orbits. How does de-Broglie hypothesis explain the stationary orbits?
(ii) Find the relation between the three wave-lengths ?₁, ?₂ and ?₃ from the energy level diagram shown below: (Delhi 2016)
Important Questions for Class 12 Physics Chapter 12 Atoms Class 12 Important Questions 74

Important Questions for Class 12 Physics Chapter 12 Atoms Class 12 Important Questions 74

Question 7.

In the study of Geiger-Marsdon experiment on scattering of a particles by a thin foil of gold, draw the trajectory of a-particles in the coulomb field of target nucleus. Explain briefly how one gets the information on the size of the nucleus from this study.
From the relation, R = R₀ \(\mathbf{A}^{1 / 3}\), where R₀, is constant and A is the mass number of the nucleus, show that nuclear matter density is independent of A. (Delhi 2015)

Question 8.

(a) Draw a schematic arrangement of Geiger- Marsden experiment showing the scattering of a-particles by a thin foil of gold. Why is it that most of the a-particles go right through the foil and only a small fraction gets scattered at large angles?
Draw the trajectory of the a-particle in the coulomb field of a nucleus. What is the significance of impact parameter and what information can be obtained regarding the size of the nucleus?
(b) Estimate the distance of closest approach to the nucleus (Z = 80) if a 7.7 MeV a-particle before it comes momentarily to rest and reverses its direction. (Comptt. Delhi 2015)

Question 9.

(a) Write two important limitations of Rutherford model which could not explain the observed features of atomic spectra. How were these explained in Bohr’s model. of hydrogen atom?
Use the Rydberg formula to calculate the wavelength of the H_? line.
(Take R = 1.1 × 10⁷ m^-1).
(b) Using Bohr’s postulates, obtain the expression for the radius of the n^th orbit in hydrogen atom. (Comptt. Delhi 2015)

Question 10.

A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. Upto which energy level the hydrogen atoms would be excited? Calculate the wavelengths of the first member of Lyman and first member of Balmer series. (Delhi 2014)